This invention relates to lenses, and, more particularly, to lenses of variable neutral density.
Imaging systems in machines such as those disclosed in U.S. Pat. Nos. 3,431,053; 3,331,181 and 3,832,057, while producing satisfactory and acceptable images, lack simple and reliable means for automatically varying the exposure control of the optical image processed through the optical systems employed. Typically, these apparatus and machines, particularly xerographic copying machines, employ photosensitive members which respond to the total exposure to which they are subjected.
The total exposure, in turn, is a product of intensity and exposure time. These aforementioned imaging apparatus and machines typically have mechanical means for adjusting exposure. An iris is used to uniformly vary the intensity while slits are used to vary the width of the exposed regions, i.e., the exposure time.
In general, liquid crystal optical states that can be utilized are those which alter the state of polarization of light. These optical states require the use of a linear polarizer and analyzer. Alteration of the state of polarization has been accomplished in uniform fashion by the mechanism of field effects.
Electro-optical field effects with liquid crystalline materials are known. Speaking generally, liquid crystalline compositions which change the state of polarization and therefore alter the passage of light therethrough when used in conjunction with a linear polarizer and an analyzer are known in the art. U.S. Pat. Nos. 3,652,148 and 3,731,986 are illustrative of field effects.